1. Field of the Invention
It is generally known that glass derives its considerable strength from a pristine or unblemished surface condition and any scratches or flaws which occur or are developed on its surface decrease its strength many fold. Normally, glass containers exhibit a maximum strength immediately upon formation, and their strength decreases as the containers come into contact with one another, and with other surfaces, such as during automatic handling.
It is well understood that if the exterior glass surfaces are coated with a composition having good wet and dry scratch resistance, as well as abrasion resistance, which characteristicly decrease the likelihood of breakage, a greater number of containers can be handled by filling and packaging equipment in the same amount of time by spacing the containers closer together and by increasing the speed of the handling conveyors, even though the glass surfaces are subjected to greater contact with like and unlike surfaces. Also, since many products such as carbonated beverages are packaged under pressure, it is highly desirable that the exterior surfaces of the glass containers have a minimal number or no scratches to minimize the possibility of breakage.
2. Description of Prior Art
Various types of single and dual surface coating compositions have been employed previously to provide abrasion and scratch resistance, as well as desired lubricity and durability to withstand handling use.
U.S. Pat. No. 3,323,889 to Carl et al relates to a method for increasing the scratch resistance of a glass surface with a pyrolyzing treatment and a coating of an olefin polymer thereover. U.S. Pat. No. 3,368,915 to Carl et al relates to an abrasion-resistant glass article having dual protective coatings thereon made by the aforesaid method. Also, U.S. Pat. Nos. 3,403,015, 3,577,257, 3,598,632, 3,645,778, 2,813,045, 2,881,566, 2,982,672, 3,258,444, 3,407,085, 3,414,429, 3,418,153, 3,418,154, 3,425,859, 3,432,331, 3,438,801, 3,441,399, 3,441,432 and 3,445,269, all relate to rendering glass surfaces abrasion-resistant and glass articles produced thereby. In none of the foregoing processes are two metal oxide forming compounds applied simultaneously with a stream of hot, dry air to form a combined metallic oxide primary coating on glass surfaces in an economical manner, where one compound is highly reactive with atmospheric moisture and the other compound is much less reactive and serves a dessicating function to shield the application of the former.